Your helmet will protect you in crashes at faster speeds too it is just tested with conditions roughly equivalent. JWC et al. would like you to believe that this means its completely worthless in higher speed crashes but that is incorrect.

Likewise pointing out that you could injure yourself in another fashion when hit by a car does not mean a helmet is worthless just that it doesn't protect against every situation. Lots of car/bike accidents end with the rider hitting his head but not causing any damage to thoracic or abdominal organs. A helmet is quite goos in such a situation.